wind effects on ‘z’ plan-shaped tall building: a case studywind tunnel study on local wind...

ORIGINAL RESEARCH

Wind effects on ‘Z’ plan-shaped tall building: a case study

Rajdip Paul1 • Sujit Kumar Dalui1

Received: 24 August 2015 / Accepted: 3 August 2016 / Published online: 17 August 2016

� The Author(s) 2016. This article is published with open access at Springerlink.com

Abstract The present paper is centered on the study to

understand the behavior of various surfaces of a ‘Z’ plan-

shaped tall building under varying wind directions. For that

purpose, computational fluid dynamics (CFD) package of

ANSYS is used. The length scale is considered as 1:300.

Force coefficients both in the along and across wind

direction as well as the external surface pressure coeffi-

cients for different faces of the object building are deter-

mined and listed for wind incidence angle 0�–150� with

increment of 30�. The wind flow pattern around the

building showing flow separation characteristics and vor-

tices are presented. The variation of wind pressure on

different surfaces of the building is clearly shown by

contour plots. The nature of deviation of external pressure

coefficients along the height of the building as well as

along the perimeter of the building for different wind

angles of attack is presented. The force coefficient (Cf)

along the X direction is extreme for 15� wind angle and

along Y direction it is maximum for 60� angle of attack.

Unsteady vortices are generated in the wake region due to a

combination of positive and negative pressure in the

windward and leeward faces, respectively.

Keywords Tall building � CFD � Wind effect �Wind angle � Force coefficient � Pressure coefficient

Introduction

As buildings are cantilever structures, there is generation of

base moment whenever it is under lateral load. The mag-

nitude of the moment increases considerably with slen-

derness, because the moment is proportional to the square

of the height of the building, just like a cantilever beam

under varying loads. Because of the scarcity of land these

days, vertical construction is given due importance and the

buildings are much higher than before, making them highly

susceptible to horizontal loading like wind load. In addition

to this, if the plan of the building is unconventional, then

wind analysis is a task of great complexity because of the

many flow situations arising from the interaction of the

wind with the structures. There are several different phe-

nomena giving rise to dynamic response of tall structures

under wind such as buffeting, vortex shedding, galloping

and flutter. Simple quasi-static analysis of wind loading,

which is globally applied to the design of low- to medium-

rise structures, can be unacceptably conservative for the

design of very tall buildings. At present, the wind tunnel

model experiment and numerical simulation using com-

putational fluid dynamics (CFD) are the available research

tools to get deeper insight into the behavior of gigantic

structures subjected to turbulent wind load.

In the definition of the overall strength, durability and

risk of failure of structures, extreme wind speed is an

important factor, mostly reliant on the general weather

pattern over many years and local environmental and

topographical conditions.

The precise evaluation of the extreme wind is mainly

connected with the quality of statistical data of wind

velocity which is associated with performance and cali-

bration of measuring instruments, common averaging time,

same height above the ground, roughness of the terrain, etc.

& Sujit Kumar Dalui

[email protected]

Rajdip Paul

[email protected]

1 Department of Civil Engineering, Indian Institute of

Engineering Science and Technology, Shibpur, Howrah,

India

123

Int J Adv Struct Eng (2016) 8:319–335

DOI 10.1007/s40091-016-0134-9

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The predicted wind speed is usually enumerated as the

maximum wind speed which is surpassed, on average, once

in every N year (return periods); for example, I.S: 875

(Part-3) (1987) requires that ordinary structures be

designed for an annual exceed probability of 2 % which is

equivalent to 50 years of return periods.

Past studies have been carried out by researchers with

the help of model analysis to get more accurate information

regarding wind structure interaction. Kareem (1986)

deliberated the details of the interference and proximity

effects on the dynamic response of prismatic bluff bodies.

Lin et al. (2004) discussed the findings of a widespread

wind tunnel study on local wind forces on isolated tall

buildings based on the experimental outcome of nine

square and rectangular models (1:500). Liang et al. (2004)

proposed the empirical formulae for different wind-in-

duced dynamic torsional responses through the analytical

model. Gomes et al. (2005) enumerated the results from the

studies of L- and U-shaped models of 1:100 scale. Lam and

Zhao (2006) examined in detail wind flow around a row of

three square-plan tall buildings closely arranged in a row at

a wind angle h = 30�. The computational domain was

digitized into 2.1 9 106 finite volumes. Irwin (2007)

reviewed a number of bluff body aerodynamic phenomena

and their effect on the structural safety and occupant

comfort. Zhang and Gu (2008) correlated the numerical

Table 1 Surface pressure coefficients for a square building

Plan of the building As per h

w

Wind angle (h) (�) Cpe for surfaces

A B C D

ANSYS CFX h

w¼ 5

0 ?0.80 -0.40 -0.60 -0.60

90 -0.60 -0.60 ?0.80 -0.40

AS-NZS 1170-2:2002Any

h

w

0 ?0.80 -0.50 -0.65 -0.65

90 -0.65 -0.65 ?0.80 -0.50

ASCE 7-10Any

h

w

0 ?0.80 -0.50 -0.70 -0.70

90 -0.70 -0.70 ?0.80 -0.50

I.S: 875 (Part-3) (1987) 3

2\

h

w\6

0 ?0.80 -0.25 -0.80 -0.80

90 -0.80 -0.80 ?0.80 -0.25

Fig. 1 Domain used for the study

Fig. 2 Plan of ‘Z’ plan-shaped building model

Fig. 3 Isometric view of the model

320 Int J Adv Struct Eng (2016) 8:319–335

123

simulation and experimental investigations of wind-in-

duced interference effects. Fu et al. (2008) enumerated the

field measurements of the characteristics of the boundary

layer and storm response of two super tall buildings. Irwin

(2009) centered on the subject of determining and con-

trolling the structural response under wind action for super

tall buildings which demand much more pragmatically

modeled wind engineering, since building codes and

standards are not practical enough for dealing with such

soaring structures. Tse et al. (2009) discussed the general

concept to determine the wind loadings and wind-induced

responses of square tall buildings with different sizes of

chamfered and recessed corners while maintaining the total

usable floor area of the building by escalating the number

of stories which is directly associated with the economics

of the building. Bhatnagar et al. (2012) presented the

results of a wind tunnel study in an open circuit boundary

layer flow condition, carried out on a model of low-rise

building with sawtooth roof. Tominaga and Stathopoulos

(2012) modeled turbulent scalar flux in computational fluid

dynamics (CFD) for near-field dispersion around buildings.

Raj et al. (2013) carried out an experimental boundary

layer wind tunnel study to observe the effect of base shear,

base moment and twisting moment developed due to wind

load on a rigid building model having the same floor area,

but different cross-sectional shapes with the variation of

wind incidence angle. Muehleisen and Patrizi (2013)

developed parametric equations to find out the values of

pressure coefficients (Cp) on the surfaces of rectangular

Table 2 Force coefficients for

the buildingPlan of the building Wind angle (�) Force coefficients Cf

Along X Along Y

0 ?0.96 ?0.01 & 0

15 ?1.02 ?0.29

30 ?0.88 ?0.52

60 ?0.73 ?1.24

90 ?0.01 & 0 ?1.04

120 -0.35 ?0.62

150 -0.61 ?0.35

Table 3 Surface pressure

coefficients for the buildingWind angle (�) Cpe (face average value) for different faces of the building

Face A Face B Face C Face D Face E Face F Face G Face H

0 0.74 0.84 0.73 -0.58 -0.41 -0.47 -0.46 -0.62

15 0.69 0.66 0.61 -0.66 -0.54 -0.52 -0.45 -0.50

30 0.73 0.29 0.36 -0.50 -0.46 -0.50 -0.44 0.06

60 -0.50 -0.55 -0.42 -0.30 -0.37 -0.48 -0.50 0.50

90 -0.64 -0.47 -0.52 -0.43 -0.61 0.06 -0.18 0.69

120 -0.57 -0.38 -0.49 -0.48 -0.64 0.74 0.81 0.53

150 -0.54 -0.41 -0.43 -0.69 -0.21 0.87 0.86 -0.37

Fig. 4 Mesh pattern around the building

Fig. 5 Name of the different faces of the building

Int J Adv Struct Eng (2016) 8:319–335 321

123

low-rise building models from experimental wind tunnel

data. Amin and Ahuja (2013) investigated through wind

tunnel studies rectangular building models of different side

ratios (ratio of building’s depth to width) ranging from 0.25

to 4, keeping the area and height the same for all models,

while the wind angle changes at an interval of 15� from 0�to 90�. Kushal et al. (2013) recognized that the plan shape

of the building affects the wind pressure to a great degree.

Verma et al. (2013) described the effects of wind incidence

angle on wind pressure distribution on square-plan tall

buildings. Bhattacharyya et al. (2014) investigated the

mean pressure distribution on various faces of ‘E’ plan-

shaped tall building through experimental and analytical

studies for a wide range of wind incidence angle. Chak-

raborty et al. (2014) enumerated the results of a wind

tunnel study and numerical studies on ‘?’ plan-shaped tall

Fig. 6 Wind flow pattern

around the building for various

wind angles


123

building and compared the results for 0� and 45� wind

incidence angles. Kheyari and Dalui (2015) have conferred

the results of a case study to estimate wind load on a tall

building under interference effects. They used a CFD

simulation tool to create a ‘virtual’ wind tunnel to predict

the wind characteristics and wind response.

Mean wind speed profiles

Wind velocity is thought to be zero at ground, and per-

sistently intensifying the mean wind speed with height can

be presented by two models: to be specific, logarithmic law

and power law. At some height, the air movement is

thought to be free from the Earth’s frictional resistance.

Height fluctuates for distinctive terrain category. The dis-

similarity in temperature offers rise to the gradients of

pressure which set air in motion.

1. Logarithmic law:

Vz

V� ¼1

kloge

z

z0

; ð1Þ

where k is the Von Karman’s constant = 0.40, z the height

above the ground, z0 the surface roughness parameter, V*

the friction viscosity =ffiffiffi

s0

q

q

, s0 the skin frictional force on

the wall and q the density of air.

2. Power law:

V

V0

¼ z

z0

� �a

; ð2Þ

Fig. 7 Variation of wind pressure on different surfaces of the building for a wind incidence angle of 0�


123

where, V is the velocity at height z above the ground, V0 the

wind speed at reference height, z0 the reference height

above the ground, generally 10 m, and a the exponent

power law, varying for different terrains.

Among these two, the power law is widely used by

researchers as it is quite easy to adjust match with mean

wind velocity profile.

Computational fluid dynamics (CFD)

Computational fluid dynamics is a computer simulation

tool that creates a ‘virtual’ wind tunnel to envisage the

motion of fluids around objects. By virtue of advance-

ments in high speed computing and parallel processing,

the CFD technique is a powerful augmentation of the

physical wind tunnel, which together enables us to solve

complex wind flow problems. CFD is a versatile and

powerful tool that can be used to solve problems related

to pedestrian-level wind comfort, cladding pressures on

buildings, etc.

There are several methods in CFD to foresee the

wind flow and their effects. Here, ANSYS CFX, AN-

SYS 14.5. ANSYS. Inc. software will be used with k–eturbulence modeling, so that decent resemblance is

maintained between the experimental and numerical

techniques. Gradient diffusion hypothesis is used in the

k–e model to relate the Reynolds stresses to the mean

velocity gradients and turbulence viscosity. ‘k’ is the

turbulence kinetic energy defined as the variance of

fluctuations in velocity and ‘e’ is the turbulence eddies

dissipation (the rate at which the velocity fluctuation

dissipates).



123

Domain size shall be suitably chosen, so that vortex

generation, velocity fluctuations, etc. in the wake region

are effectively conformed. Revuz et al. (2012) suggested

that inlet, outlet, two side face and top clearances of the

domain be 5H, 15H, 5H and 5H, respectively, from the

edges of the buildings, where ‘H’ is the height of the

building. The domain is shown in Fig. 1. A combination of

tetrahedron meshing and hexagonal meshing shall be

considered for meshing the domain and the surface of the

building model. Finer hexagonal meshing around and on

the surfaces of the building is obtained by providing

inflation, which leads to simulate uniform flow and mea-

sure the actual behavior of the responses accurately. Uni-

form coarser tetrahedron meshing in the rest of the domain

will considerably reduce the time of analysis without sig-

nificant loss of accuracy.

Validation of CFD

Validation of the CFD package has been done by ana-

lyzing a square building model using ANSYS CFX.

From the available information of I.S: 875 (Part-3)

(1987) for a simple square building of particular aspect

ratio (h/w = 5), the pressure coefficients can be evalu-

ated from the respective tables. Thereafter, numerical

analysis was conducted in the ANSYS CFX software for

a similar building model under comparable wind



123

environment to obtain these coefficients on different

faces of the building. This evaluation obviously can be

done on the basis of any other international standard of

wind load.

Table 1 shows the comparison of the external pressure

coefficient Cpe between different standards of various

countries and Cpe calculated by ANSYS CFX for a square

building. The results of the numerical analysis resembles

the provisions of the code AS-NZS 1170-2:2002, Aus-

tralian/New Zealand Standard, ‘‘Structural design actions,

part 2: wind actions’’ and ASCE Standard (ASCE/SEI

7-10) ‘‘Minimum design loads for buildings and other

structures’’, with good agreement. For the windward face,

there is 0 % deviation in the result, whereas for the

sidewalls the deviation is 7.7 and 14.3 % with respect to

AS-NZS 1170-2:2002 and ASCE 7-10, respectively. But

for the leeward face, the result from ANSYS deviates by

20 % with respect to both the codes. This deviation in

result is perhaps due to the generation of unsteady vortices

in the wake region near the leeward face.

Parametric model of the study

The present study will be carried out to understand the

behavior of pressure distribution on the various surfaces of

a ‘Z’ plan-shaped building with varying wind directions.

The building has clear dimensions of each limb with



123

100 mm length and 50 mm width (Fig. 2). The limbs are

orthogonal to each other. The height of the building is

considered as 500 mm. The plan area of the building is

22,500 mm2 consequently. The rigid model length scale is

considered as 1:300. The isometric view of the model is

shown in Fig. 3. The domain and meshing used are as

discussed in the preceding section. The mesh pattern

around the building is shown in Fig. 4.

Results and discussion

The numerical study of the model as stated before has been

done by the k–e turbulence model using ANSYS CFX. The

domain, meshing and flow pattern are considered as

discussed earlier. Different faces are named for reference

as shown in Fig. 5. The directions of the wind considered

are indicated also in the same figure.

External force and pressure coefficientsfor the building

Force coefficients (Cf) along the X and Y direction are

determined using the formula Cf = F/(P 9 A), where ‘F’

is the total force exported from numerical simulation in the

desired direction corresponding to the wind angle, ‘P’ is

the wind pressure and ‘A’ is the surface area exposed to the

wind. Wind incidence angle 0�–150� with an interval of

30� is considered. An additional wind angle 15� is also



123

considered. The coefficients are presented in Table 2. The

force coefficient along the X direction is maximum for a

15� wind angle and the same along Y is maximum for a 60�wind angle of attack. A negative sign indicates suction. The

wind pressure obtained by the computational method using

the ANSYS CFX is used to calculate the external pressure

coefficient ‘Cpe’ using the formula Cpe ¼ P=ð0:6V2z Þ,

where Vz is the design wind speed and ‘P’ is the wind

pressure. The external surface pressure coefficients, Cpe

(face average value), for different faces of the building are

listed in Table 3. Positive pressure coefficients occur at the

windward faces because of direct wind dissipation and

suction pressure at the leeward faces due to frictional flow

separation and vortex generation.

The wind flow pattern around the building for different

wind incidence angles is shown in Fig. 6. Flow separation

characteristics and vortices are quite evident from the flow

patterns. The variations of wind pressure on different sur-

faces of the building for wind angles 0�, 15�, 30�, 60�, 90�,120� and 150� are shown in Figs. 7, 8, 9, 10, 11, 12 and 13,

respectively. Referring to Fig. 14a–g, it is quite clear that

the Face A, Face B and Face C being the windward faces

for wind incidence angle 0� are subjected to positive

pressure, of which Face A has the lowest face average Cpe



123

because of the uplift force and backwash. Face D, Face E,

Face F, Face G and Face H are exposed to suction pressure.

Again, positive pressure occurs at Face A, Face B and Face

C for 15� wind angle of attack. But in this case, Face A has

the maximum Cpe at a certain height and also maximum

face average Cpe among faces having positive pressure

because of reduced backwash effect. Other faces are sub-

jected to suction pressure again. The nature of variation of

Cpe along the height of the building can be seen from the

graph and face average values are available in Table 3. For

30� wind angle, there is positive pressure on Face B up to a

certain height and then it suffers suction pressure. Face A is

purely under positive pressure. The variation of Cpe for

Face H is almost linear. The pressure is positive, but of

very low (face average Cpe is 0.06) magnitude. When the

wind incidence angle is increased to 60�, Face A, Face B

and Face C, which are exposed to positive pressure up to

30� wind angle, are now changed to suction pressure. All

the faces, except Face H, are subjected to negative pressure

now. In case of 90� wind angle, the pressure at Face F is

positive for some height and then decreases to negative. At

greater height, it touches positive pressure again and ulti-

mately suction at the top. This results in small face average

Cpe of 0.06 for Face F. The pressure is positive for Face H

and there is suction pressure for the rest of the faces. When

the wind angle of attack is 120�, Face F, Face G and Face

H become windward faces and are subjected to positive

pressure, while the other faces are exposed to suction

pressure. The maximum positive pressure occurs at Face F

and the maximum negative pressure at Face E. For wind

angle 150�, there is an interesting scenario of overlapping

pressure variations along the height for Face F and Face G.

The pressure variation is positive for both the faces and the

face average Cpe is almost same consequently. The



123

deviation of pressure is wide for Face E. There is non-

uniform variation of suction pressure up to a certain height

for this face and thereafter the pressure becomes positive.

The other faces are under more or less uniform negative

pressures.

The variation of wind pressure along the horizontal

centerline of all the faces of the building for wind angles

0�, 15�, 30�, 60�, 90�, 120� and 150� are shown in Figs. 15,

16, 17, 18, 19, 20 and 21 respectively. Three different

heights of the building are considered to take into account

Fig. 14 Variation of pressure

coefficients along the vertical

centerline on different faces for

various wind angles


123

the variation along the height as well. The ordinate of the

graph is the external pressure coefficient (Cpe) of each face

and along the abscissa the perimeter of the building is

plotted. These plots support understanding the overall

scenario, i.e., the response of all the faces of the building

under a particular wind incidence angle. For 15� wind

Fig. 14 continued


123

Fig. 15 Comparison of

pressure coefficients along the

horizontal line through various

faces at three different heights

of the building for 0� wind angle





of the building for 15� wind

angle






angle


123






angle






angle






angle


123

angle, even though Cpe is positive for Face A, Face B and

Face C, there is a sudden fall in Cpe at Face B for the height

of 470 mm. It touches suction pressure and then rapidly

becomes positive again. This may be a result of uplift force

at a greater height of the building. For 30�, the nature of

variation is more or less similar. The Cpe values changes

with height only. From the plots, the backwash effects at

the lower portion of the building and uplift at greater height

are quite clear.

Conclusion

Provisions of the codes are usually available for orthog-

onal wind directions only. But the results of the study

clearly indicate that for tall buildings, a deeper perception

of the phenomenon of wind structure interface is needed

for more precise information. For that, model analysis is

inevitable. The force coefficient (Cf) along the X direction

has a maximum value of 1.02 for 15� wind angle and the

same along Y is extreme for the 60� wind angle of attack

with a value of Cf equal to 1.24. Quite obviously, the

windward faces are subjected to positive pressure coeffi-

cients because of the undeviating wind force. Because of

frictional flow separation and generation of vortices, the

leeward faces are exposed to suction. Flow separation

characteristics and vortices are quite apparent from the

streamlines. The pressure force on the windward side and

suction force on the leeward side in combination produce

vortices in the wake region, causing the deflection of the

body. There may be occurrence of suction even on the

windward faces because of the separation of flow in

structures with limbs and also due to uplift, sidewash and

backwash of wind.

Open Access This article is distributed under the terms of the

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tivecommons.org/licenses/by/4.0/), which permits unrestricted use,

distribution, and reproduction in any medium, provided you give

appropriate credit to the original author(s) and the source, provide a

link to the Creative Commons license, and indicate if changes were

made.

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